Means of preserving metallic surfaces



Patented Apr. 19, 1932 UNITED STATES PATENT OFFICE LAKES C. VIGNOS, OFNITRO, WEST VIRGINIA, ASSIGNOR TO THE RUBBER SERVICE LABORATORIESCOMPANY, OF AKRON, OHIO, A CORPORATION OF OHIO MEANS OF IRE-SERVINGMETALLIC SURFACES Ito Drawing. Original application filed January 14,1928, Serial No. 246,917. Divided and this application filed January 14,1928. Serial No. 246,918.

The present invention relates to the cleaning and preservation of ametallic surface wherein the surface is in contact with liquids of anacid nature. More particularly, the invention relates to the preventionof excessive pitting and embrittlement of metals when subjected to apickling process. The invention includes the provision of a regulator orinhibitor for causing the acid solution selectively to attack uncleanportions of metallic surfaces immersed therein to the substantialexclusion of any corrosive action upon the clean portions of the metalsurface.

In the art of pickling, the metal is treated with a dilute acid toremove rust, scale or other deposits. The acid solution removes the rustand scale, but in the absence of any material preventing such action,also attacks clean portions of the metal thereby causing pitting orover-pickling of the portions of the metallic surface. Such pitting isparticularly detrimental and undesirable when the metal is to be plated,painted or galvanized and cold worked.

By means of the present invention the objectionable features of thepickling process are substantially overcome and eliminated. Toaccomplish this in accordance with the present invention. there is addedto the pickling bath or other acid solution employed, a regulating agentor ingredient which acts to restrain the action of the acid in removingthe scale or deposits. or in other words. the ingredient causes the acidselectively to remove oxides and the like without materiallv attackingthe clean portions of the metal surface.

The regulators or inhibitors which are d sclosed in the presentapplication comprise organic sulfur-containing con poundsof a type fifgatiibiidlfutQflfims .are...io edc. aa single carbonlatom rsuehcarbombeing also ink''dto a' nitrogen atom. Such compounds are designated asthiuram sulfids and include mono and disulfid compounds represented asfollows:

and

s BPINHB posed which duplicated, so far as possible,

those commonly followed in commercial practice, so far as concerned acidconcentrations and temperatures employed. The heating of the metallictest strips in the pickling liquor in the manner as hereinafter setforth was, however, from three to four times that ordinarily followed inpractice for the acid concentrations employed.

Test pieces of steel approximately three inches square were cut from asheet after the annealing process had been carried out. The steelemployed had a carbon content of approximately 0.04%. These pieces werethen immersed in approximately 500 cc. of sulfuric acid solutioncontaining approximately 8% by weight of 66 Baum acid together with asmall quantity of one of the preferred type of inhibitor. Although thequantity of inhibitor taken may vary between relatively wide limits, ithas been found that particularly favorable results are realized when theproportion of inhibitor is from 0.01 to 0.1 of 1% of the weight of theacid solution employed.

The test pieces were subjected to the action Examine of the pickleliquor for approximately 9.1

10 strength specified above but containing no inbltor. Comparisons ofthe loss in weight sufi'ered by the various test pieces give at once ameasure of the inhibiting action exerted by the compounds tested.

Thiuram mono and disulfids, which as hereinbefore indicated contain thegrouping S\ or g ll scribed. An acid solution of the strength mentionedand containing only 0.002% by weight of the inhibitor was found to beparticularly effective for the object desired. Such a solution was foundto pickle iron and steel strips in such a manner that the acid loss dueto solvent action of the acid was only 3.8% as great as that takingplace when no inhibitor was employed. This loss distributed over thearea of surface exposed to the pickle solution amounted to only 0.00066grams per square inch as compared with a loss of 0.01722 grams persquare inch when no inhibitor was employed.

Other thiuram sulfids have also been found to possess a desirableinhibiting effect when employed in quantities comprising less than 1% ofthe pickle solution. Thus, tests similar to those hereinbefore set forthhave been carried out wherein ligthyl-dihen I, disulfid, eth l thi ram m-m @flp eridyl 1ur thelikewere employedas respectivelv have been foundto be effective inhibitors and found to retard the action of forpreventing excessive deterioration of metals immersed in or subjected tothe action of an acid solution. Thus a solution was prepared for use inpickling metals comprising 500 cc. of sulfuric acid containingapproximately 8% by weight of 66 Baum. To this acid solution there was added about 0.01

grams of di-allyl thiura in disulfid. The resulting mtainedapp'roximately 0.002% of the disulfid. Iron test strips were thenimmersed in the solution for about sixty minutes while maintaining thesolution at a temperature of from 80 to 85 C. The loss in weight of thetest strips resulting from exposure to the pickling solution wasobserved to be only about 7.5% of the loss that resulted when asimilartest strip was pickled under the same conditions in an acid solutioncontaining no inhibitor. That is. the inhibitor decreased by about 13/14the metal loss due to solvent action of the acid on the metal. This losswhen calculated on the surface exposed to the solution amounted to but0.00155 grams per square inch of surface exposed as compared with a lossof 0.0172 grams per square inch where no inhibitor was employed.

A similar test carried out in the manner as described, except thatdimethyl-alphau ease-211m .esc place ofthe inhibitor spebiii''d in theexample,

yielded a result showing that the solvent action of the acid on themetal was decreased by approximately 12/13. In other words, the loss inmetal per square inch of surface exposed to the acid solution was but0.0013

grams as compared with a loss of 0.017 2 grams per square inch where noinhibitor was employed.

A further test was completed wherein dia eth ll l-thiuram disulfid wasemp oyed as an inhibitor in the manner as deacid upon a metal. Byproceeding in a like manner, similar beneficial effects were ascertainedto be exercised when thiuram disulfids were employed in a pickle liquorcomprising hydrochloric acid. Other metals such as copper and the likewere also protected from undue corrosion by acids when the preferredtype of inhibitors were employed in the pickling liquor. It is evidentfrom the various examples hereinbefore set forth, that thiuram mono anddisulfids comprise a class of effective inhibitors in processes whereinmetals are subjected to the action of an acid. Greater inhibiting actionhas been found to be produced by the use of a larger quantity of thevarious compounds than that set forth in the examples. It is not,however, necessary to employ an acid solution containing more than 1 byweight of the inhibiting compound nor is it desirable to use a greaterquantity than will completely dissolve in the solution emploved.

The examples hereinbefore set forth are to be understood as illustrativeonly and not at all limitative of the scope of the invention. Otherexamples of the process 'described are apparent to those skilled in theart to which the invention pertains wherein different acidconcentrations, times of treatment and temperatures may be employed. Theinvention is to be considered as limited solely by the following claimswherein the invention is claimed as broadly as possible in view of theprior art.

This application is a cation Serial No. 246,917

What is claimed is:

1. The process of cleaning a metal surface which comprises treating suchmetal with sulfuric acid solution containing a small proportion of athiuram disulfid.

division of applifiled on even date.

2. The process of cleaning a metal surface 252. COMPOSITIONS,

which comprises treating such metal with a sulfuric acid solutioncontaining a small proportion of a dialkyl-diaryl-thiuram-disulfid.

3. The process of cleaning a metal surface which comprises treating suchmetal with a sulfuric acid solution containing a small proportion of adiethyl-di-o-tolyl-thiuram-disulfid.

4. A pickling bath for iron and steel products comprising a pickle acidcontaining a dissolved dialkyl-diaryl thiuram compound.

5. A pickling bath for iron and steel products comprising sulfuric acidcontaining a dissolaved diethyl-di-o-tolyl thiuram compoun 6. A picklingbath for iron and steel products comprising sulfuric acid containingfrom 0.01% to not more than 1% of dissolved diethyl di-o-tolyl thiuramdisulfid.

7. A pickling bath for iron and steel products comprising a pickle acidcontaining an aryl substituted thiuram disulfid.

In testimony whereof I hereunto afiix my signature.

JAMES C. VIGNOS.

Examiner

